Centrifugal fan

ABSTRACT

There is provided a centrifugal fan including an upper casing which has an air suction opening, a lower casing, and an impeller which is disposed between the upper casing and the lower casing. The impeller includes an upper shroud which is provided on an upper casing side, and a plurality of blades which are arranged along a circumference direction below the upper shroud, and is rotatable around a rotary shaft. A pressure surface of each of the plurality of blades has a convex shape in a rotation direction and is formed with a plurality of protrusions which extend in parallel with the rotary shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a centrifugal fan, and moreparticularly, to a centrifugal fan having a casing and an impeller.

2. Description of the Related Art

A centrifugal fan (centrifugal blower) is a fan for blowing air in aradial direction by rotating an impeller including a plurality of blades(also referred to as wings, impeller). One of this kind of fans is acentrifugal multi-blade fan which includes a casing having a suctionopening and a discharge opening and accommodating therein an impellerhaving a plurality of blades around a rotary shaft of a motor. Thecentrifugal multi-blade fan suctions air from the suction opening,allows the air flow through the blades from the center of the impeller,and discharges the air outward in the radial direction of the impellerby a centrifugal action from the rotation of the impeller. The airdischarged from the outside of the outer circumference of the impellerpasses through the casing while increasing the pressure of the air, andthe high-pressure air is discharged from the discharge opening.

These centrifugal multi-blade fans are widely used for cooling,ventilation, and air-conditioning in home appliances, OA equipment, andindustrial equipment, and in blowers for vehicles and the like. Theblowing performance and noise of such centrifugal multi-blade fan arelargely affected by a blade shape of an impeller and a shape of acasing.

The following patent application publications disclose improvement inblade shapes of fans, for example.

JP-A-H11-247795 discloses an impeller of a centrifugal fan, and theimpeller has a plurality of ridges which is formed on a surface of eachblade oriented at a rotation direction such that the ridges aresubstantially parallel with a rotary shaft.

JP-A-H11-294386 discloses an impeller of a centrifugal fan, and theimpeller has a plurality of ridges which is formed on a surface of eachblade at a rotation direction such that the ridges are substantiallyparallel with a rotary shaft and the widths and heights of the ridgesincrease from a side plate toward a main plate.

JP-A-2005-16315 discloses a centrifugal fan which includes a side plateand a main plate provided inside a casing, and a plurality of bladesannularly disposed on the main plate. On the back side of each blade ina cross-section of the blade perpendicular to a rotary shaft, aplurality of ridges and grooves are provided from the leading edge ofthe blade toward the tailing edge of the blade.

JP-A-2001-32794 discloses a centrifugal fan which includes a fan mainbody having a number of blades arranged along a circumference direction,and a motor for rotating the fan main body, and discharges air from theinner side toward the outer side in the radial direction of the fan byrotation of the fan main body. The blades have ridges (or grooves)formed on a negative pressure surface at a downstream in the rotationdirection.

As apparatuses have been reduced in sizes and thicknesses, haveincreased in assembly densities, and have been reduced in powerconsumption, it has been strongly required from the market to improvestatic pressures and efficiency for fan motors for those apparatuses. Asfor fans, it is also important to reduce noise. Particularly,related-art centrifugal fans tend to cause high discrete frequency noise(narrowband noise) and high wideband noise, so that large noise iscaused when the centrifugal fans are installed in apparatuses.

Here, the discrete frequency noise is noise based on a blade passingfrequency, and is also called as NZ noise. The discrete frequency noiseis noise having a characteristic peak at a specific frequency of anarrow frequency band. This frequency can be expressed by the equation:fnz=n (rotational frequency)×z (number of blades). Since not only theprimary component but also the secondary and higher components occur,the discrete frequency noise becomes a big problem even in actualhearing. In other words, when those centrifugal fans are installed inapparatuses, there is a risk that noise might occur as clear sound.Also, since a turbulent flow is a dominant factor of wideband noise, anddetermines a total noise level, it is also required to reduce thewideband noise.

Further, in addition to implementation of the above requirements, it isalso required to improve the productivity of fans.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances,and it is an object of the present invention to provide a centrifugalfan which can suppress noise.

According to an illustrative embodiment of the present invention, thereis provided a centrifugal fan comprising: an upper casing which has anair suction opening; a lower casing; and an impeller which is disposedbetween the upper casing and the lower casing, wherein the impellerincludes an upper shroud which is provided on an upper casing side, anda plurality of blades which are arranged along a circumference directionbelow the upper shroud, and is rotatable around a rotary shaft, andwherein a pressure surface of each of the plurality of blades has aconvex shape in a rotation direction and is formed with a plurality ofprotrusions which extend in parallel with the rotary shaft.

In the above centrifugal fan, the plurality of protrusions may bedensely formed in an area in the vicinity of a leading edge of eachblade and not formed in an area in the vicinity of a base part of eachblade.

In the above centrifugal fan, the plurality of protrusions may protrudefrom the pressure surface and satisfy at least one of conditions: thenumber of protrusions for each blade is 3 or more and 15 or less; andthe diameter of each of the protrusions is larger than 0 mm and is equalto or less than 1 mm.

In the above centrifugal fan, the plurality of protrusions may have asemicircular shape as seen in a direction parallel to the rotary shaftand satisfy at least one of conditions: the number of protrusions foreach blade is 10; a pitch between adjacent protrusions is 1.5 mm; andthe diameter of each of the protrusions is 0.5 mm.

In the above centrifugal fan, the upper casing and the lower casing mayconfigure an open-type casing, the impeller further may include a lowershroud which is provided below the plurality of blades, an outsidediameter of the lower shroud may be equal to or smaller than an insidediameter of the upper shroud, and an inside portion of each of theblades may have an inclined portion which connects an inside circleportion of the upper shroud and an inside circle portion of the lowershroud.

According to the above configuration, it is possible to provide acentrifugal fan which can suppress noise.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view illustrating a centrifugal fan according toa first illustrative embodiment of the present invention;

FIG. 2 is a view illustrating the longitudinal section of the middle ofthe centrifugal fan of FIG. 1;

FIG. 3 is a perspective view illustrating an impeller 3 as seen from aside of the upper shroud 23;

FIG. 4 is a view illustrating a blade shape of the centrifugal fan ofFIG. 1 as seen from a side of the upper shroud 23;

FIG. 5 is a cross-sectional view taken along a line A-A of FIG. 4;

FIG. 6 is a cross-sectional view taken along a line B-B of FIG. 4;

FIG. 7 is a cross-sectional view taken along a line C-C of FIG. 4;

FIGS. 8A and 8B are views illustrating the cross-section shape and noisecharacteristic of a related-art impeller, respectively;

FIGS. 9A and 9B are views illustrating the cross-section shape and noisecharacteristic of the impeller according to the first illustrativeembodiment of the present invention, respectively;

FIG. 10 is a cross-sectional view illustrating an impeller of acentrifugal fan according to a modified illustrative embodiment;

FIG. 11 is a perspective view illustrating a centrifugal fan accordingto a second illustrative embodiment of the present invention;

FIG. 12 is a view illustrative the longitudinal section of the middle ofthe centrifugal fan of FIG. 11;

FIG. 13 is a view illustrating an air flow between an upper shroud andan upper casing of the centrifugal fan shown in the section of FIG. 2;

FIG. 14 is a view illustrating an air flow between an upper shroud andan upper casing of the centrifugal fan shown in the section of FIG. 12;

FIG. 15 is a view illustrating the air flow-pressure characteristics ofthe centrifugal fan shown in the section of FIG. 2 and the centrifugalfan shown in the section of FIG. 12;

FIG. 16 is a view illustrating a cross section structure of acentrifugal fan according to a modified illustrative embodiment;

FIG. 17 is a cross-sectional view illustrating the centrifugal fanaccording to a modified illustrative embodiment;

FIG. 18 is a cross-sectional view illustrating a half of a centrifugalfan according to a third illustrative embodiment of the presentinvention;

FIG. 19A is a bottom view of an impeller according to a fourthillustrative embodiment, and FIG. 19B is an enlarged view illustrating aportion ‘B’ of FIG. 19A;

FIG. 20 is a side view illustrating the impeller of FIG. 19;

FIG. 21 is a view illustrating a method of measuring a radius of eachprotrusion and a pitch (interval) between adjacent protrusions;

FIG. 22 is a view illustrating forming positions of the protrusions in ablade;

FIG. 23 is a view illustrating the static pressure-air flow (P-Q)characteristics of the impeller according to the first illustrativeembodiment (comparative example) shown in FIGS. 1 to 7 and the impelleraccording to the fourth illustrative embodiment (embodiment); and

FIG. 24 is a view illustrating noise characteristic of the impelleraccording to the fourth illustrative embodiment (embodiment) forcomparing with the impeller according to the first illustrativeembodiment (comparative example) shown in FIG. 9B.

DETAILED DESCRIPTION

Hereinafter, illustrative embodiments of the present invention will bedescribed with reference to the accompanying drawings.

First Illustrative Embodiment

FIG. 1 is a perspective view illustrating a centrifugal fan according toa first illustrative embodiment of the present invention, and FIG. 2 isa view illustrating a longitudinal section at a middle part of thecentrifugal fan of FIG. 1. FIG. 3 is a perspective view illustrating animpeller 3 as seen from a side of an upper shroud 23, and FIG. 4 is aview illustrating a blade shape of the centrifugal fan of FIG. 1 as seenfrom the side of the upper shroud 23. FIGS. 5 to 7 are cross-sectionalviews taken along lines A-A, B-B, and C-C of FIG. 4, respectively.

Referring to FIGS. 1 to 4, in a centrifugal fan 1, a central impeller 3rotates to blow air. The impeller 3 includes seven blades 2 disposed atregular intervals, and rotates around a rotary shaft 11 by a fan motor13 provided in the centrifugal fan 1. The direction of the rotation is aclockwise direction in FIG. 4.

The impeller 3 is accommodated in a casing 4. The casing 4 is configuredby an upper casing 5 and a lower casing 6 which have plate shape, and inorder to place the upper casing 5 and the lower casing 6 evenly spacedapart from each other, four columnar supports 7 are provided at fourcorners of the casing 4, respectively. At the top of the centrifugal fan1, an air suction opening 8 is formed. Air discharge openings 9 areprovided between the respective columnar supports 7 of the casing 4. Inother words, the air discharge openings 9 are provided at four sides ofthe casing 4 in four directions (open casing type). The casing 4 mayhave one discharge opening for collecting air discharged from theimpeller 3 in one direction (scroll casing type).

As shown in FIGS. 2 to 7, the impeller 3 has an annular lower shroud 21,an annular upper shroud 23, and a plurality of blades 2 which arearranged along a circumference direction between the lower shroud 21 andthe upper shroud 23, and is rotatable around the rotary shaft 11.

As shown in FIG. 4, the annular lower shroud 21 has an inside circle 21Aand an outside circle 21B in a planar view. The inside circle 21A andthe outside circle 21B are circles in a planar view. The annular uppershroud 23 has an inside circle 23A and an outside circle 23B in a planarview. The inside circle 23A and the outside circle 23B are circles in aplanar view. The outside circle 21B of the lower shroud 21 overlaps theinside circle 23A of the upper shroud 23. In other words, the outsidecircle 21B of the lower shroud 21 is the same as the inside circle 23Aof the upper shroud 23. However, the outside circle 21B of the lowershroud 21 may be slightly smaller than the inside circle 23A of theupper shroud 23.

In FIG. 4, the shape of each blade 2 seen from the internal space of theinside circle 23A of the upper shroud 23 is shown by a solid line.Further, the shape of each blade 2 hidden between the inside circle 23Aand outside circle 23B of the upper shroud 23 by the upper shroud 23 isshown by a dotted line.

As shown in FIG. 4, each blade 2 has a shape tapering from the inside(rotary shaft) to the outside in a planar view. In other words, eachblade 2 has a shape becoming thinner as separating further from therotary shaft 11. Each blade 2 has an inlet angle of 45° and an outletangle 22°. The diameter of the outside circle 23B is 120 mm, and thediameter of the inside circle 21A is 70 mm. The blades 2 are backwardinclined blades.

As shown in FIGS. 3 to 7, the upper portion of each blade 2 is fixed tothe lower surface of the upper shroud 23, and the lower portion of eachblade 2 is fixed to the upper surface of the lower shroud 21. Here,since the outside circle 21B of the lower shroud 21 is designed to bethe same as the inside circle 23A of the upper surface (or the outsidecircle 21B of the lower shroud 21 is smaller than the inside circle 23Aof the upper surface), it is possible to integrally form the impeller 3only by using upper and lower molds.

As shown in FIGS. 4 to 7, the inside circle side (the side close to therotary shaft) of the upper portion of each blade 2 is connected to theinside-circle-side end portion of the upper shroud 23. From thisposition to the outside-diameter-side end portion of the upper portionof each blade 2, the upper portion of each blade 2 is connected to thelower surface of the upper shroud 23. In other words, as shown in FIG.4, in a range where the upper shroud 23 and the blades 2 exist (a placesurrounded by a dotted line) in a planar view, the upper shroud 23 is incontact with the blades 2.

Further, the lower portion of each blade 2 is connected to the lowershroud 21.

As shown in FIG. 5, the inside circle side of the upper portion of eachblade 2 is connected to the inside-circle-side end portion of the uppershroud 23. The upper portion of each blade 2 has a tapered portion(inclined portion) from that position toward the inside circle side. Inother words, the inside circle portion of each blade 2 has an inclinedportion which connects the inside circle portion (inside-circle endportion) of the upper shroud 23 and the inside circle portion of thelower shroud 21.

The tapered portion of each blade 2 forms an inclined surface having anangle γ of 42° with respect to a vertical direction. In FIG. 4, aportion of each blade 2 shown by a solid line is a tapered portion, anda portion of each blade 2 shown by a dotted line shows a portion inwhich the upper portion of the corresponding blade 2 is connected withthe upper shroud 23. Further, the portion of each blade 2 shown by thesolid line shows a portion in which the lower portion of thecorresponding blade 2 is connected with the lower shroud 21. The portionof each blade 2 shown by the dotted line shows a portion in which thelower portion of the corresponding blade 2 is not connected with thelower shroud 21 (a portion below which the lower shroud 21 does notexist).

The angle γ, which is 42° in FIG. 5, is called a taper angle, and theangle γ is not limited to 42°.

In the impeller 3, in a portion in which the upper shroud 23 exists in aplanar view, the lower shroud 21 does not exist. Therefore, it ispreferable to provide a protrusion 6 a at the upper portion of the lowercasing 6 as shown in FIG. 2 such that the protrusion 6 a protrude upwardand takes place of the lower shroud 21 at the portion of the impeller 3in which the lower shroud 21 does not exist. The protrusion 6 a isformed at the portion where the upper shroud 23 exists (the portionwhere the lower shroud 21 does not exist) in a planar view such that adistance between the lower portion of each blade 2 and the lower casing6 becomes shorter. The protrusion 6 a protrudes to a height at which thelower shroud 21 exists. In this way, it is possible to allow the lowercasing 6 to have a structure for acting as the lower shroud.

In the above-mentioned impeller 3, the inside circle portion of eachblade 2 has a tapered shape. The base portion of the tapered portion isintegrated with the lower shroud 21. The upper portion of each blade 2is entirely integrated with the upper shroud 23 except for the taperedportion. Further, as shown in FIG. 5, the inside diameter Dl of theupper shroud 23 is the almost the same as the outside diameter D2 of thelower shroud 21 (D1≈D2) or may be larger than the outside diameter D2 ofthe lower shroud 21 (D1>D2). This shape makes it possible to integrallyform the impeller 3 only by upper and lower molds and provide thehigh-productivity impeller 3 and the high-productivity centrifugal fan1.

Further, since it is unnecessary to increase or decrease the diameter ofthe air suction opening, it is possible to suppress a static pressureand an air flow from being reduced.

Furthermore, in the centrifugal fan 1 according to this illustrativeembodiment, it is possible to improve an air flow by the tapered shapeof each blade 2. Moreover, it is possible to cover the suction openingportion with the shrouds. Therefore, it is possible to reduce noise.This feature will be described below.

FIGS. 8A and 8B are views illustrating a cross-sectional shape and noisecharacteristic of a related-art impeller, respectively.

As shown in the cross-sectional view of FIG. 8A, a related-art impeller3′ includes a lower shroud 21′, an upper shroud 23′, and a plurality ofblades 2′ disposed between the lower shroud 21′ and the upper shroud23′. The outside circle of the lower shroud 21′ is the same as theoutside circle of the upper shroud 23′. Therefore, it is not possible tointegrally form the impeller 3′ only by upper and lower molds.

FIG. 8B shows a noise characteristic during driving of the impeller 3′of FIG. 8A by taking frequencies on a horizontal axis and noise values(dB(A)) on a vertical axis.

Noise is 58.0 dB(A) in total, and both of discrete frequency noise andwideband noise (turbulence noise) shows high values as shown in FIG. 8B.

FIGS. 9A and 9B are views illustrating a cross-sectional shape and noisecharacteristic of the impeller according to the illustrative embodimentof the present invention, respectively.

As shown in the cross-sectional view of FIG. 9A, the impeller 3according to the present illustrative embodiment includes the lowershroud 21, the upper shroud 23, and the plurality of blades 2 disposedbetween the lower shroud 21 and the upper shroud 23. The outside circleof the lower shroud 21 is almost the same as the inside circle of theupper shroud 23. Therefore, it is possible to integrally form theimpeller only by upper and lower molds.

FIG. 9B shows a noise characteristic during driving of the impeller ofFIG. 9A by taking frequencies on a horizontal axis and noise values(dB(A)) on a vertical axis.

Noise is 57.3 dB(A) in total. Further, as shown in a solid line circleof FIG. 9B, discrete frequency noise (the primary and secondary noise ofthe blades) is lower than that in FIG. 8B. Furthermore, as shown in adotted line circuit of FIG. 9B, wideband noise (turbulence noise) isalso lower than that in FIG. 8B.

FIG. 10 is a cross-sectional view illustrating an impeller of acentrifugal fan according to a modified illustrative embodiment.

An impeller 3 according to the modified illustrative embodiment isdifferent from the impeller shown in FIGS. 1 to 7 in that a base plate(plate) 21 a for extending the outside circle of the lower shroud 21outward is attached at the lower portion of the impeller 3. The diameter(inside diameter) of a hollow portion of the base plate 21 a is the sameas the outside diameter of the lower shroud 21. The outside diameter ofthe base plate 21 a is the same as the outside diameter of the uppershroud 23. Therefore, it is possible to make the outside circle of theupper shroud 23 coincide with the outside circle of the base plate 21 a,and to secure the same P-Q characteristic as that of the configurationof the impeller 3 as shown in FIGS. 8A. In other words, the base plate21 a functions as an appendant lower shroud. Since the base plate 21 ais attached, it is also possible to reduce noise while maintaining theP-Q characteristic.

Even in this modified illustrative embodiment, the portion of theimpeller 3 except for the base plate 21 a can be integrally formed onlyby upper and lower molds, such that the productivity of the impeller isimproved.

[Other(s)]

The fan according to the illustrative embodiment is adaptable to allcentrifugal fans such as a turbo type, a multi-blade type, and a radialtype. The fan can be mainly installed in products requiring suction andcooling (such as home appliances, PCs, OA equipment, and in-vehicleequipment) and the like.

Effect(s) of Illustrative Embodiment

As described above, the impeller according to the illustrativeembodiment, the upper shroud does not overlap the lower shroud at all ina planar view. Therefore, it is possible to manufacturing the impellerby integral molding using upper and lower molds, and thus theproductivity of the impeller is high.

The upper portion of the inside circle portion of each blade contactsthe top of the upper shroud. The inside circle portion of each bladelowers from that position to a lower portion with an inclination (thetaper angle γ), so that the lower portion of the inside circle portionof the corresponding blade comes into contact with the lower shroud.Therefore, the diameter of the suction opening does not increase, andthus the highest static pressure is not reduced.

Further, according to the illustrative embodiment, it is possible tomake an efficient blade shape in view of an air flow such that a flowincreases, the static pressure increases, and noise is reduced.

Second Illustrative Embodiment

FIG. 11 is a perspective view illustrating a centrifugal fan accordingto a second illustrative embodiment of the present invention, and FIG.12 is a view illustrating the longitudinal section of the middle of thecentrifugal fan of FIG. 11.

The centrifugal fan of FIG. 11 is different from the centrifugal fan ofFIG. 1 in a structure of an upper casing 5A. That is, the upper casing5A has an upper surface formed with a plurality of recesses 54, and ribs52 between the adjacent recesses 54.

The plurality of recesses 54 are formed to surround the rotary shaft 11.The ribs 52 are formed radially around the rotary shaft 11. The numberof the recesses 54 is 16 as shown in FIG. 16. The number of ribs 52 isalso 16. The number of recesses 54 or ribs 52 is not limited thereto.

As shown in FIG. 12, the upper surface of the upper shroud 23 (thesurface facing the upper casing 5A) has a portion (first portion) whichbecomes closer to the lower casing 6 as separating further from therotary shaft 11. In this portion, the upper surface of the upper shroud23 has a curved surface.

Each recess 54 is shallow at a portion close to the rotary shaft 11 andis deep at a portion away from the rotary shaft 11, such that the bottomsurface of the recess 54 connecting the two portions becomes a curvedsurface. The thickness of a portion between the bottom surface of eachrecess 54 and the lower surface of the upper casing 5A (the surfacefacing the upper shroud 23) on a side of the upper casing 5A opposite tothe bottom surface of the recess 54 is kept constant. In this portionwhere the thickness is kept constant, the lower surface portion (secondportion) of the upper casing 5A has a curved surface which has almostsame shape as (or is the same as) that of the bottom surface of therecess 54. In other words, the curved surface of the first portion isalmost same as (or is same as) the curved surface of the second portion.

According to this configuration, the centrifugal fan according to theillustrative embodiment has the following features.

(1) The lower surface of a case (the upper casing 5A) having the airsuction opening 8 has a shape having a curvature which is close to (orthe same as) that of the upper surface of the upper shroud 23.Therefore, air coming from a discharge opening side of the impeller 3can be suppressed from flowing back toward the suction opening 8 in aspace between the upper casing 5A and the upper shroud 23. Therefore,deterioration of the characteristic of the fan can be prevented.

(2) If the lower surface of the upper casing 5A is formed simply in theshape described in (1), the upper casing 5A becomes thick. However,since the recesses 54 are provided, it is possible to prevent the uppercasing 5A from becoming thick (it is possible to reduce the use of amaterial). Instead of the recesses 54, one recess having a doughnutshape with the center at the rotary shaft 11 may be formed. In thiscase, if the ribs 52 are provided at predetermined angular intervals, itis possible to give a constant rigidity to the upper casing 5A.

(3) As the impeller 3, any one of the impellers of FIGS. 1 to 10 may beused (even a related-art impeller may be used). Further, the shape ofthe blades 2 is arbitrary.

FIG. 13 is a view illustrating an air flow between an upper shroud andan upper casing of the centrifugal fan shown in the section of FIG. 2,and FIG. 14 is a view illustrating an air flow between an upper shroudand an upper casing of the centrifugal fan shown in the section of FIG.12.

As shown in FIG. 13, in a case where the surface of the upper casing 5facing the impeller 3 is flat, a small room is formed between theimpeller 3 and the upper casing 5, and a portion of air discharged fromthe impeller 3 flows back in the small room toward the air suctionopening 8. Further, a portion of the back-flow air swirls inside thesmall room.

In contrast, as shown in FIG. 14, if the recesses 54 are provided to theupper casing 5A such that the surface of the upper casing 5A facing theimpeller 3 has a shape with the same curvature as that of the uppershroud of the impeller 3, it is possible to suppress (improve) a backflow of air.

FIG. 15 is a view illustrating the air flow-pressure characteristics ofthe centrifugal fan shown in the section of FIG. 2 and the centrifugalfan shown in the section of FIG. 12.

In FIG. 15, the characteristic of the centrifugal fan shown in thesection of FIG. 12 is shown by a mark of ‘PRESENT EMBODIMENT (BACK-FLOWPREVENTION CASE)’, and the characteristic of the centrifugal fan shownin the section of FIG. 2 is shown by a mark of ‘RELATED ART (FLATCASE)’. That is, the structure of the upper casing 5 having the flatlower portion shown in FIG. 2 is called as a flat case, and thestructure of the upper casing 5A shown in FIG. 12 is called as aback-flow prevention case.

As shown in FIG. 15, if the structure for preventing a back flow of airis used, it is possible to improve the characteristic of the fan.

FIG. 16 is a view illustrating a cross section structure of acentrifugal fan according to a modified illustrative embodiment, andFIG. 17 is a cross-sectional view illustrating the centrifugal fanaccording to the modified illustrative embodiment.

The centrifugal fan according this modified illustrative embodiment isconfigured by forming flanges 56A and 56B for attachment of thecentrifugal fan, integrally with the upper casing 5A of the fan shown inFIGS. 11 and 12. The flanges 56A and 56B are formed with screw holes.Therefore, it is possible to easily attach the fan to another componentby inserting screws into the screw holes. One or more flanges may beprovided, and it is possible to facilitate attachment of the fan.

Third Illustrative Embodiment

FIG. 18 is a cross-sectional view illustrating a half of a centrifugalfan according to a third illustrative embodiment of the presentinvention. This centrifugal fan uses an impeller shown in FIGS. 3 to 7.

Referring to FIG. 18, the centrifugal fan according to the thirdillustrative embodiment includes an impeller 103 having a plurality ofblades 104, and a casing which houses the impeller 103. The impeller 103is rotationally driven by a motor 102.

The impeller 103 includes the plurality of blades 104 arranged along acircumferential direction at regular intervals and an annular shroud 105which supports one end sides of the blades 104. On the other-end sidesof the blades 104, a main plate is not provided. An upper surface of theannular shroud 105 is formed as a predetermined curved surface, and acylindrical portion 109 is formed at the center of the shroud 105. Theinner side of the cylindrical portion 109 configures an air suctionopening.

The impeller 103 has a cup-shaped boss section 106 at the center thereof. The blades 104 have a curved shape with a predetermined curvatureand all are formed in the same shape. The blades 104 are backwardinclined blades, have a blade shape inclined backward with respect to arotation direction, and configure a turbofan. The blades 104, theannular shroud 105, and the boss section 106 are formed of a syntheticresin by integral molding. To the inner side of the cup-shaped bosssection 106, a rotor of the motor 102 is jointed. As the rotation of themotor 102, the impeller 103 rotates.

The casing has a quadrangular shape. The casing has an upper plate 111made of a synthetic resin and having a circular opening at the center.In the vicinities of four corner portions of the upper plate 111,substantially cylindrical supporting columns are provided, respectively.At the periphery of the opening of the upper plate 111, a foldingportion 112 is formed to protrude downward. On the inner side of thefolding portion 112 (the rotary shaft side of the impeller 103), thecylindrical portion 109 of the shroud 105 is disposed with apredetermined interval.

A motor base 114 is disposed to face the upper plate 111. Between theupper plate 111 and the motor base 114, the four supporting columns areinterposed. The upper plate 111 and the supporting columns are jointedby joint members 128 (such as bolts, screws, rivets, and the like). Thesupporting columns and the motor base 114 are jointed by joint members128 (such as bolts, screws, rivets, and the like). The supportingcolumns and the upper plate 111 may be formed by integral molding, andthe supporting columns and the motor base 114 may be jointed by thejoint members 128.

Portions surrounded by adjacent supporting columns of the plurality ofsupporting columns, the upper plate 111, and the motor base 114 becomeopenings. The openings become air discharge opening.

As described above, all of the four sides of the casing of thecentrifugal fan according to the present illustrative embodiment havethe openings. In other words, the sides of the casing are configured byonly the supporting columns (the openings are formed at portions exceptfor the supporting columns).

The outside diameter of the impeller 103 to be housed in the casing isset to be smaller than the dimension of one side of the casing. In acase where the outside diameter of the impeller 103 is larger than thedimension of one side of the casing, since the rotating impeller 103protrudes from the outer edge of the casing, there are fears such ascontact with other members and damage due to contact, which is notpreferable. For this reason, it is preferable to set the outsidediameter of the impeller 103 such that the impeller 103 does notprotrude from the outer edge of the casing.

The motor 102 is an outer rotor type brushless motor. The rotor isconfigured by a cup-shaped rotor yoke 125, a ring-shaped magnet 127, anda shaft 107. The magnet 127 is fixed to the inner circumferentialsurface of the rotor yoke 125. The shaft 107 is fixed to a boss 126formed at the center portion of the rotor yoke 125.

The shaft 107 is supported to be rotatable by one pair of bearings 119installed in a bearing holder 118. On the outer circumferential surfaceof the bearing holder 118, laminated stator cores 120 are mounted. Onthe stator cores 120, an insulator 122 with a coil 121 wound thereon ismounted. The bearing holder 118 is mounted on the motor base 114. Thestator cores 120 mounted on the bearing holder 118 is disposed to facethe magnet 127 in the radial direction (the horizontal direction of FIG.18) with a predetermined gap. The motor base 114 is formed by pressing ametal plate (for example, an iron plate). The motor base 114 has aquadrangular shape, similarly to the casing, and has a recess 115 formedat the center. The peripheral edge is bent in an axial direction (thevertical direction of FIG. 18) to form a side plate 116. Since the sideplate 116 is formed, it is possible to improve the rigidity of the motorbase 114. At the center of the recess 115 of the motor base 114, anopening is formed. The bearing holder 118 is mounted in the opening ofthe recess 115, and the motor 102 is housed in the recess 115.

The blades 104 of the impeller 103 jointed to the rotor yoke 125 aredisposed to face a flat surface portion 117 of the motor base 114 in theaxial direction (the vertical direction of FIG. 18) with a gap having apredetermined length G. In other words, the impeller 103 has theplurality of blades 104 such that at least a part of a lower portion ofeach blade 104 is exposed to the flat surface portion 117 of the motorbase 114. The lower portion of each blade 104 may be entirely exposed tothe flat surface portion 117 of the motor base 114. A lower surface ofthe insulator 122 has a PCB board 123 attached thereto. The PCB board123 has an electronic component 124 mounted thereon for controlling themotor 102.

If the impeller 103 rotates by driving of the motor 102, air issuctioned from the air suction opening, passes through the blades 104 ofthe impeller 103, and is discharged toward the outer side in the radialdirection of the impeller 103 by a hydrodynamic force based on acentrifugal action according to the rotation of the impeller 103.

The motor base 114 has the function of a main plate (lower shroud) whichis provided at the bottom of an impeller in the related-art structure,and also has the function of a lower plate of the casing (lower casing).Therefore, it may be important to setting the length G of the gap formedbetween the impeller 103 and the flat surface portion 117 of the motorbase 114. In a case where the gap length G is excessively large, airsuctioned from the inlet flows even in the gap while passing through theblades 104. As a result, the pressure of the air discharged from theblades 104 is reduced, and thus an air flow characteristic is reduced.Meanwhile, in a case where the gap length G is excessively small, if avariation occurs in the accuracy of the dimensions of each component, itis feared that the blades 104 of the impeller 103 will come into contactwith the flat surface portion 117 of the motor base 114. In order toprevent this contact, it is necessary to manage the accuracy of thedimensions of each component, and thus the cost of the centrifugal fanincreases.

As described above, the gap length G is an important factor having aneffect on the air flow characteristic of the centrifugal fan.Specifically, the gap length G is set in view of the air-flowcharacteristic and cost of the centrifugal fan. In a related-artcentrifugal fan having a scroll casing, the noise was 61 dB(A). Incontrast, in the centrifugal fan according to the present illustrativeembodiment, when the length G of the gap between the impeller 103 andthe flat surface portion 117 of the motor base 114 was set to 0.5 mm,the noise was 58 dB(A). That is, according to the present illustrativeembodiment, it is possible to suppress the noise.

Fourth Illustrative Embodiment

FIG. 19A is a bottom view of an impeller according to a fourthillustrative embodiment of the present invention, and FIG. 20 is a sideview illustrating the impeller of FIG. 19A. FIG. 19B is an enlarged viewillustrating a portion ‘B’ of FIG. 19A.

The impeller according to the present illustrative embodiment has thesame configuration as that of the impeller shown in FIGS. 1 to 14 and 16to 18 except that protrusions are provided on pressure surfaces ofblades. Specifically, a pressure surface of each blade 2 has a convexshape in the rotation direction, and is formed with a plurality ofprotrusions (ridges) 2 a which extend in parallel with the rotary shaft.This impeller can be disposed between an upper casing (correspond to theupper plate 111 in FIG. 18) disclosed with respect to FIGS. 1, 2, 11,12, and 16 to 18, and a lower casing (correspond to the motor base 114in FIG. 18), whereby a centrifugal fan can be configured.

The plurality of protrusions 2 a are densely formed in an area in thevicinity of the leading edge (on the outer side) of each blade 2, andare not formed in an area in the vicinity of the base (on the innerside) of each blade 2. In FIGS. 19A to 20, ten protrusions 2 a areformed at each blade 2, and the intervals (pitches) between theprotrusions are the same. Further, as shown in FIGS. 19A and 19B, theprotrusions 2 a protrude from the pressure surface of each blade, andhave a semicircular shape in a plan view. As shown in FIG. 20, eachprotrusion 2 a is a stripe-shaped protrusion extending from the upperedge portion to the lower edge portion of a corresponding blade 2.

FIG. 21 is a view illustrating a method of measuring a radius of eachprotrusion 2 a and a pitch (interval) between two adjacent protrusions.

The protruding height H of a protrusion from a pressure surface isreferred to as a radius of the protrusion in a plan view, and aninterval between adjacent protrusions is referred to as a pitch P. Theheight H is also ½ of the diameter (hereinafter, referred to as adiameter of the protrusion) of a circle obtained by extrapolating fromthe semicircular shape of the protrusion in the plan view. If the heightH, the pitch P, and the number of protrusions change, the staticpressure-air flow (P-Q) characteristic and noise of the fan would changeas follows. Therefore, it is possible to obtain the optimal fancharacteristic by adjusting the height H, the pitch P, and the number ofprotrusions, which will be described below.

Experiments were conducted while changing the number of protrusions foreach blade so as to obtain various static pressure-air flow (P-Q)characteristics, air flows, and noises.

According to the following manner, it was found that an impeller is anoptimum embodiment, in which the number of protrusions for each blade is10, the pitch P is 1.5 mm, and the protrusion diameter is 0.5 mm (theheight H is 0.25 mm) in a plan view.

Compared to the impeller of the optimal embodiment (embodiment) having10 protrusions (ridges) for each blade, a comparative example A1 having3 protrusions (ridges) for each blade, a comparative example A2 having15 protrusions (ridges) for each blade, a comparative example A3 having20 protrusions (ridges) for each blade, and a comparative example A4having 25 protrusions (ridges) for each blade were prepared, and graphsrepresenting the static pressure-air flow (P-Q) characteristics andnoises of the embodiment and the comparative examples were obtained.

Although the number of protrusions changed, the static pressure-flow(P-Q) characteristics were within a range of error. The noise was thelowest when the number of protrusions for each blade was 10. Also, itwas seen that the noise is reduced when the number of protrusions foreach blade is 3 or more and 15 or less. As compared to a case where thenumber of protrusions (the number of ridges) for each blade is 0, thenoise is significantly reduced in a case of forming protrusions.

Experiments were performed while changing the pitch between adjacentprotrusions so as to obtain various static pressure-air flow (P-Q)characteristics, flows, and noises.

Compared to the impeller of the optimal embodiment (embodiment) having apitch P of 1.5 mm, a comparative example A5 having a pitch P of 1 mm, acomparative example A6 having a pitch P of 2 mm, and a comparativeexample A7 having a pitch P of 2.5 mm were prepared, and graphsrepresenting the static pressure-air flow (P-Q) characteristics andnoises of the embodiment and the comparative examples were obtained.

Although the pitch P changed, the static pressure-air flow (P-Q)characteristics were within the range of error. The noise was the lowestwhen the pitch P is 1.5 mm.

Experiments were performed while changing the diameters of protrusionsso as to obtain various static pressure-air flow (P-Q) characteristics,flows, and noises.

Compared to the impeller of the optimal embodiment (embodiment) havingprotrusion diameters R of 0.5 mm, a comparative example A8 havingprotrusion diameters R of 1 mm, and a comparative example A9 havingprotrusion diameters R of 1.5 mm were prepared, and graphs representingthe static pressure-air flow (P-Q) characteristics and noises of theembodiment and the comparative examples were obtained.

In a high static pressure area, the static pressure-air flow (P-Q)characteristic was the best when the diameters were 0.5 mm. Further, thenoise was the lowest when the diameters were 0.5 mm. Also, it was seenthat, in a case where the diameter of each of a plurality of protrusionsis larger than 0 mm and is equal to or less than 1 mm, there is aneffect of reducing a certain degree of noise.

FIG. 22 is a view illustrating a protrusion forming position of eachblade.

As shown in FIG. 22, when the impeller having 10 protrusions for eachblade is formed such that the pitch P is 1.5 mm and the diameter of eachprotrusion is 0.5 mm (the height H of each protrusion is 0.25 mm), ifthe length of each pressure surface from the outer circumferentialsurface 21B of the lower shroud (which is equal to the innercircumferential surface 23A of the upper shroud) to the leading edgeportion of a blade 2 is L1, the length of the pressure surface from theouter circumferential surface 21B of the lower shroud to the position ofthe innermost protrusion 2 a in the radial direction is L2, and thelength of the pressure surface from the position of the outermostprotrusion 2 a in the radial direction to the leading edge portion ofthe blade 2, L1 is 56 mm, L2 is 40 mm, and L3 is 2.6 mm. In other words,the plurality of protrusions 2 a are densely formed in an area in thevicinity of the leading edge of each blade 2, and is not formed in anarea in the vicinity of the base of each blade 2. Also, it is known byan experiment that it is preferable to set the ratio of L2 to L1 to 50%or more and to set the ratio of L3 to L1 to about 0% to 10%.

FIG. 23 is a view illustrating the static pressure-air flow (P-Q)characteristics of the impeller (comparative example) according to thefirst illustrative embodiment shown in FIGS. 1 to 7 and the impeller(embodiment) according to the fourth illustrative embodiment. Also, FIG.24 is a view illustrating the noise characteristic of the impelleraccording to the fourth illustrative embodiment (embodiment) forcomparing with the impeller according to the first illustrativeembodiment (comparative example) shown in FIGS. 9A and 9B.

As shown in FIG. 23, the static pressure-air flow (P-Q) characteristicrarely changed due to provision of the protrusions. As described above,the noise in FIG. 9 was 57.3 dB(A) overall, but the noise in FIG. 24 was54.3 dB(A) overall. From this, it was seen that the noise is improved by3.0 dB(A) by providing the protrusions.

[Others]

The impeller according to the fourth illustrative embodiment is notlimited to the turbo type, but can be used for all centrifugal fans suchas a multi-blade type and a radial type. The impeller can be preferablyused for products requiring suction and cooling (such as homeappliances, PCs, OA equipment, and in-vehicle equipment).

The shape of each protrusion in the plan view is not limited to asemicircular shape, but may be a triangular shape, a rectangular shape,a polygonal shape, a wedge type, and so on. At each blade, two or moreprotrusions may be provided. Also, in a case where three or moreprotrusions are provided to each blade, the protrusions may be providedat regular pitches (such that the distances between every two adjacentprotrusions are the same) or at irregular pitches (such that thedistances between every two adjacent protrusions are different).

The protrusions may be provided at the leading edge portion, centerportion, or tailing end portion of each blade, or may be an entiresurface of each blade. A plurality of assemblies of protrusions 2 a asshown in FIG. 22 may be formed at each blade.

It is preferable to integrally form the protrusions by a mold for resinmolding such that the protrusions are parallel with the direction of therotary shaft.

The above-mentioned illustrative embodiments should be considered asillustrative in all aspects, but not restricting. The scope of thepresent invention is defined by the appended claims rather than theforegoing description, and is intended to include all modifications inthe equivalent meaning and range to the scope of the claims.

What is claimed is:
 1. A centrifugal fan comprising: an upper casingwhich has an air suction opening; a lower casing; and an impeller whichis disposed between the upper casing and the lower casing, wherein theimpeller includes an upper shroud which is provided on an upper casingside, and a plurality of blades which are arranged along a circumferencedirection below the upper shroud, and is rotatable around a rotaryshaft, and wherein a pressure surface of each of the plurality of bladeshas a convex shape in a rotation direction and is formed with aplurality of protrusions which extend in parallel with the rotary shaft.2. The centrifugal fan according to claim 1, wherein the plurality ofprotrusions are densely formed in an area in the vicinity of a leadingedge of each blade and not formed in an area in the vicinity of a basepart of each blade.
 3. The centrifugal fan according to claim 1, whereinthe upper casing and the lower casing configure an open-type casing,wherein the impeller further includes a lower shroud which is providedbelow the plurality of blades, wherein an outside diameter of the lowershroud is equal to or smaller than an inside diameter of the uppershroud, and wherein an inside portion of each of the blades has aninclined portion which connects an inside circle portion of the uppershroud and an inside circle portion of the lower shroud.